Both early and late protection by ischemic preconditioning (PC) is elicited by a number of triggers and mediators. Among them, nitric oxide (NO) derived from NO synthase is believed to be responsible for both early and late PC. The downstream signaling pathways that translate into synthesis of cardioprotective proteins remain largely unknown. The central hypothesis of this proposal is that late PC is the result of NOS upregulation by initial ischemic stimulus via a signaling cascade involving PKC and NFkappaB with mitochondrial KATP channel as the end effector of protection. The uniqueness of this study is that it identifies the mitochondrial KATP channel as the end effector of protection both in early and late PC. To address this issue, we propose to determine whether 1) PC by mitoKATP channel is due to NO formation via iNOS upregulation, 2) late PC by mitoKATP channel involves NFkappaB-iNOS pathway, 3) late PC is mediated by opening of mitoKATP channel via PKC signaling pathway, 4) PKC stimulation is caused by NO during mitoKATP channel activation, 5) late PC by mitoKATP channel reduces cell injury by inhibiting apoptosis, and 6) late PC by mitoKATP channel attenuates ischemic injury by maintaining mitochondrial membrane potential. To accomplish these aims, we will use normal rats and transgenic mice lacking iNOS, eNOS, nNOS, NFkappaB, PKCdelta and PKCepsilon. The role of PKCdelta and PKCepsilon in mitoKATP-mediated protection will be evaluated in genetically manipulated mice. NOS knockout mice will be important to rule out nonspecific effects of NO on mitoKATP channel. A wide range of multidisciplinary techniques including biochemistry, cell biology, molecular biology, electron microscopy, immunocytochemistry and pharmacological approaches will be used to integrate the information at the cell level with the function at the organ level. Isoform-specific PKC translocation, NOS mRNA, isoform expression and activities will be examined both during early and late PC. This proposal is the first which will identify mitoKATP channel as an end effector of protection during PC and will have important implications for designing pharmacological and gene therapeutic interventions against the lethal ischemia.